Tube cap



FIG. 1 is a perspective view of a tube cap showing my new design;

FIG. 2 is a front elevational view thereof, the rear elevational view, the right side view, and the left side view being the same; and,

FIG. 3 is a top plan view thereof.

The bottom and interior of the bottle cap form no part of the claimed design. 

The ornamental design for a tube cap, as shown and described. 